Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$16.25	7.382%	$17.4496	$17.45	$17.45	$17.40
Purchase #2	$143.82	3.259%	$148.5071	$148.51	$148.50	$148.50
Purchase #3	$178.81	10.814%	$198.1465	$198.15	$198.15	$198.10
Purchase #4	$84.86	6.375%	$90.2698	$90.27	$90.25	$90.30
Purchase #5	$106.46	11.330%	$118.5219	$118.52	$118.50	$118.50
Purchase #6	$129.31	6.349%	$137.5199	$137.52	$137.50	$137.50
Purchase #7	$226.80	11.863%	$253.7053	$253.71	$253.70	$253.70
7 purchase totals =	$886.31		$964.1201	$964.13	$964.05	$964.00